For over 15 years now, I’ve faithfully kept a diary. Every night, from age 11 until my senior year of university, I snuggled into my bedsheets and rehashed the day’s events before nodding off to sleep. Even though I’m more likely to scribble down my thoughts just once or twice a week nowadays, I’ve found that writing in a diary before bed is a fun way to capture my memories – no matter how frivolous – to enjoy again years down the road.

Now a new study, published recently in The Quarterly Journal of Experimental Psychology, suggests that my nightly routine might help with something else: being able to recall a specific day’s events from memory weeks later. Importantly, however, I may be at a greater advantage than some diarists because I typically write in my diary just before hitting the pillow, instead of waiting until the next morning.

Cognitive psychologist Ágnes Szőllősi and her colleagues were interested in exploring how autobiographical memories, or personal memories of one’s life experiences, can be influenced by the time at which they’re recorded and consolidated. Because it’s known that sleep has a beneficial effect on learning and long-term memory formation, the authors hypothesised that people who recorded the day’s events in the evening just before bed would recall more events 30 days later than those who chronicled their day the next morning.

To test this, Szőllősi and her colleagues recruited 109 young adults between the ages of 18 and 25 to keep a written diary online. The age range was purposely narrow to control for circadian effects, as young people tend to perform better at tasks in the evening than older adults.

The participants were divided into three groups: those who recorded their notes in the evening, just before bed, about an event that they had experienced earlier that same day (Group 1); those who recorded in the morning, right after waking, an event from the previous day (Group 2); and those who recorded in the evening, just before bed, an event from the previous day (Group 3). In addition to keeping their diary for five consecutive days, participants also rated the personal importance of the events they’d written about (on a scale of 1 to 5), the duration of the events, and the amount of sleep they’d had the night before.

Thirty days later, all participants were instructed to describe as many of the previously-recorded events as they could, and how certain they were about their recollections (on a scale of 1 to 5). “Recall rate” was then calculated as the percentage of recalled events out of those recorded initially in the online diary.

Importantly, there were no differences between the groups in the way that they kept their diaries: the number of recorded events, the length of descriptions (word count), ratings of personal importance, and duration of the events, were the same for all three groups. Nor were there any group differences in the amount of time the participants reported sleeping.

And yet, recall rate was nearly 10 per cent lower in Group 2 – these were the participants who chronicled the previous day’s events in the morning after awakening – compared to the two evening groups. Despite differences in how the groups performed, however, the three groups scored similarly in ratings of certainty – in other words, the evening diarists didn’t seem to know their memories were more accurate. Also, the evening benefit applied to all event memories equally, regardless of their personal significance.

The researchers concluded that the time of memory reactivation (in this case, the time at which an event is described in a diary) affects how the memories are reconsolidated. But why? Szőllősi and her colleagues suggest that when a memory is in an “unstable” form (which is what happens after reactivation – in this case, after writing about an event in a diary), it’s vulnerable to interference. When participants wrote in their diary in the morning, interfering events that took place later in the day could disrupt the consolidation process. However, when done right before bed – whether on the day of the event or even 24 hours later – sleep may work to re-stabilise and consolidate these memories.

To examine this hypothesis further – and given the effect of age on circadian preference – it would be interesting to re-run this experiment in older adults, as they tend to perform better on memory and cognitive tasks in the morning compared to young adults.

The new results might be useful if you’re considering using a daily diary as a way to keep happy memories alive – such as on holiday, say, or charting a special period in your child’s development. By recording your reflections in the evening rather than the morning, you’ll be carving the memories deeper in your own mind.

However, my own motives are different – I’ll keep up my diary habit mostly because I’m eager to see how 50-year-old Jordan will eventually interpret the mind of 11-, 18-, and 25-year-old Jordans.